First I think it would matter if you were a man or a woman. I've not heard the term snappy casual but I was a fashion cop for hire once. For a man, I'd suggest something with a little color or print either an aloha shirt and solid pants (if overweight alot) or plaid pants and a cool polo (if you have a memorable waistline). If that is too drastic for your taste, perhaps you could consider the ever sexy man's ensemble of a great white shirt, tucked into nice fitting jeans and leather shoes. I would avoid showing your man toes, if you are a man.
If you are a woman I would think dressing snappy would not be the same as dressing casual as you might for gardening, lounging in front of the tv or sloppy sort of wear. As a gal, I'd probably go with nice white pants and a vivid top, sandals, or a casual fabric skirt with a unmatched but coordinated top.
No Flip Flops! For either gender you can't miss going with some sort of Brooks Brothers look style look; khakis, nice button down, cotton shirt in a nice stripe. Since it is a business thing you are attending I would strongly avoid anything sloppy, flip flops, too short, or short shorts. ....Longer style, dressier shorts for women might be appropriate, but only if you have nice looking legs, in general I think most men and women look absolutely dreadful in shorts. Newer fashion shorts for women can look great on a slim figure, or the super short ones only on a young 20 something with great legs, with great shoes, with a top that covers more. Too much bareness not cool for work.